Household cooking devices using a microwave, so-called microwave ovens, have been commonly used. Nowadays, cooking devices using steam, especially superheated steam that is highly effective for removing fat and salt contained in food, are also common. There are two types of cooking devices using steam: those which use only steam for cooking and those which use a microwave and steam in combination.
Regardless of whether cooking is performed using a microwave or steam, leakage of a microwave and steam from a heating chamber may cause safety problems, and thus various measures have been taken to prevent such leakage. A measure commonly taken to prevent leakage of a microwave is to provide a choke structure as described in Patent Publications 1 to 4 (listed below). When a choke structure is provided at the door of a heating chamber, leakage is prevented relatively effectively at the sides of the door, but it is not easy to prevent leakage at the corners of the door. To cope with this, in the device described in Patent Publication 1, the choke provided at the four corners of the door is designed to have a particular longitudinal width. In the device described in Patent Publication 2, a slit-choke structure is provided in an area where an upper or a lower hinge overlaps the door body. In the device described in Patent Publication 3, the bending angle at which a bent section is bent is larger near a corner than at other locations. In the device described in Patent Publication 4, protruding surface sections located near the corners of the door are designed to protrude more than those in other locations. In order to prevent leakage of steam, a gasket is commonly used as described in Patent Publications 5 and 6.    [Patent Publication 1] JP-A-2003-243150 (Pages 2 to 4, FIGS. 1 and 2)    [Patent Publication 2] JP-A-2003-109745 (Pages 2 and 3, FIGS. 1 to 10)    [Patent Publication 3] JP-A-H8-124674 (Pages 3 and 4, FIGS. 1 to 4)    [Patent Publication 4] JP-A-H7-94272 (Pages 3 and 4, FIGS. 1 to 5)    [Patent Publication 5] JP-A-2000-30856 (Pages 2 and 3, FIGS. 1 to 4)    [Patent Publication 6] JP-A-H2-178524 (Page 2, FIGS. 1 to 5)